Rotating electrical machines in the form of turbogenerators are used in power stations for generating electrical energy. For this purpose, a turbogenerator is mechanically coupled to at least one gas turbine and/or a steam turbine, wherein the turbogenerator together with the gas turbine forms a turbo set.
During the operation of a rotating electrical machine, heat is unavoidably generated in the stator and/or the rotor of the rotating electrical machine. This heat loss occurs as a result of converting mechanical energy into electrical energy by means of the rotating electrical machine.
In order to achieve a reliable operation of the rotating electrical machine, it is necessary to dissipate the heat that is generated in a stator and/or rotor of a rotating electrical machine out of the rotating electrical machine. This is in particular necessary owing to the fact that electrical insulation is present on the stator and/or on the rotor and said insulation becomes impaired after achieving a specific temperature, which could lead to damaging electrical short circuits. The more heat that is dissipated out of a rotating electrical machine, the more the capacity of the rotating electrical machine can be used, which accompanies a corresponding increase in power.
Conventionally, a cooling fluid in the form of surrounding air, water, hydrogen and/or a mixture that contains hydrogen is used to dissipate heat from a rotating electrical machine or to cool the stator and/or the rotor of the rotating electrical machine. The cooling fluid is introduced axially between the stator and the rotor at the two axial ends of the rotating electrical machine and is mostly dissipated in the center of the rotating electrical machine radially out of the rotating electrical machine.
Heat is typically not generated in a stator and/or a rotor of a rotating electrical machine in a uniform manner. That is to say that there are regions of the rotating electrical machine in which more heat is generated than in other regions of the rotating electrical machine. The regions in which more heat is generated and/or that are not sufficiently cooled are also described as “hot spots”. In hot spots of this type, it is possible by means of the heat that is generated as a result of the operation for impermissible and damaging overheating to occur more rapidly than in regions of a rotating electrical machine that are influenced by less heat. As a consequence, a conventional rotating electrical machine can only be used to its capacity if the materials that are arranged in the hot spots render possible a reliable operation of the rotating electrical machine.
It is also disadvantageous in the case of the conventional use of a cooling fluid, by way of example in the form of surrounding air, so as to dissipate heat, that when reaching a hot spot, the surrounding air has already absorbed so much heat that originates from other regions of a rotating electrical machine that a sufficient cooling arrangement of a hot spot is no longer possible. Consequently, it is possible by means of conventional heat dissipation, in particular using surrounding air, to ensure a more reliable operation of a rotating electrical machine in a more reliable permanent manner only up to a capacity upper limit that is dependent upon the heat load that is present in the hot spots.